Why did you start w/ 1.9? Nevermind. I assume by "white screens" you mean that happens before you get to the EZV's menu, yes? If it's when you try to launch a game that's a whole 'nother ball of wax and it likely means that you've recycled your SD from another cart (or an early EZV kernel) and it patched the roms in a way that the EZV 2.0 kernel doesn't like.
Anyway, I'm guessing at this point you don't have anything of value on the SD card (ie saves and such, back'em up if you). Just format it (FAT 32) and install the kernel on the clean SD. You should be OK.
If it was working before under the V12 firmware and 1.9 there is no reason why it shouldn't work w/ 2.0RC4. The situation suggests that how ever you installed 2.0 goofed something up your kernel install on your SD... None of which is unfixable.